Abstract : This invention relates to rotary shaft decoupling devices and more particularly to an improved shaft decoupler device of the type that can be actuated to rapidly decouple a driven apparatus, such as a generator, from its prime mover. While not limited thereto, the present invention finds application in association with aircraft generators wherein it is desirable for the flight engineer to be able to positively decouple a generator from the aircraft engine, and to be assured that recoupling will not occur.